DE2420558C2 - Process for the manufacture of conductors for optical signals - Google Patents

Description

The invention relates to a method for producing conductors for optical signals.

From DE-OS 19 632 a manufacturing method for optical fibers is known in which from heat-treated Jar of composition

R _x O · B ₂ O ₃ · QO ₂ ,

wherein R ₁ O is an alkali, alkaline earth or heavy metal oxide, χ denotes the number 1 or 2 and QO ₂ denotes silicon or germanium oxide, a preform is drawn which is subjected to a heat treatment for phase separation and then treated with an acidic aqueous solution until the B ₂ O ₃ · R ₂ O phase has dissolved out of the surface layer of the preform. In this way, the B ₂ O ₃ · R ₂ O phase is retained in the core of the glass fiber, so that the thickness of the surface layer is between 20 and 50%, based on the original radius. Accordingly, pores can only arise in this surface layer, and the low-SiO ₂ phase still contained in the fiber core with the impurities accumulated therein cannot be separated from the preform. However, these impurities affect the optical properties of optical signal guides made from such preforms.

US Pat. No. 21 06 744 also describes a treated borosilicate glass which is melted from a starting mixture of 75% SiO ₂ , 5% Na ₂ O and 20% B ₂ O ₃ and shaped according to the intended use. The molded parts are then heated until the glass phase separates. The molded parts are then treated with aqueous acid solutions until the more easily soluble low-silicate phase is completely or partially dissolved out of the molded part. What remains is the molded part as a porous skeleton of the silicate-rich phase

can be subjected to a sintering heat treatment to close the pores. On the other hand, can this porous molded part for technical purposes, for example as a semipermeable membrane or as a catalyst carrier can be used.

It is known, however, that the most suitable means of transmission for optical signals is optical fiber. In such an optical guide the light beam is confined and is transmitted through a solid glass fiber of cylindrical cross-section, with a plurality of glass fibers combined into a bundle and are protected by a sheath so that the conductor can be handled like a cable. The single ones Fibers usually consist of an inner glass vein, which is provided with an upper pull, which is a smaller one Has refractive index than the glass vein, so that the light beam entering at one end of the fiber bundle is enclosed in the glass vein and is continued therein by total internal reflection. The diameter such glass veins is approximately between 1 and 100 µm and the typical ratio of the upper draw diameter is on the order of 1.1 to 1.

Another type of glass fiber for guiding optical waves are so-called self-focusing fibers a radially parabolic index of refraction that causes the light beam to travel along the fiber is constantly focused. The desired course of the refractive index is attempted using an ion exchange technique to achieve by, for example, thallium ions near the surface of the glass fiber Sodium or potassium ions are replaced. With this type of ladder it is very difficult to find the one you want To achieve ion distribution, and long times are required for ion exchange.

The preferred constituents of the glasses for optical fibers are generally silicates. The raw materials from which the glass components are obtained can be of various types such as oxides or carbonates, but must be of high purity. In particular, transition metals such as ferrous ions, nickel or Chromium, to be largely excluded; they must preferably only be used in an amount of less than 2 ppb are present.

To produce the fibers, fibers are drawn from a melt. This happens either after the Standard double crucible process or by means of preforms made from tubes or rods of suitable size (Amer. Cerm. Soc. BuIU Vol. 49 (1970), pp. 969-973).

In the production of self-focusing fibers, the drawn fiber can be used for ion exchange directly be passed through a molten salt bath.

In the production of optically conductive glass fibers for use as a transmission medium in communication systems over long distances, efforts are made to produce silicate fibers with little signal loss by means of a relatively inexpensive, economical production process. One of the problems is reducing the loss through external absorption, that is, absorption through the presence of molecular or ionic impurities, particularly Fe ⁺⁺ and other transition elements. Manufacturing processes that attempt to solve this problem are expensive and complicated by the effort to keep or separate the iron contaminants from the silicate glasses. The iron gets into the glass both via the raw materials and during the melting process. An example of this is the vapor deposition technique (US-PS 37 11 262).

The invention is based on the object of a method for producing such conductors for optical signals indicate the free of the starting materials introduced into the glass and the transmission of the signals interfering impurities, these conductors can and only be self-focusing show little loss by external absorption.

This object is achieved according to the invention by a method for producing conductors for optical Signals consisting of a core with a coating layer whose refractive index is smaller than that of the Core, by drawing a preform from the melt of a glass of the pseudo-ternary system

45 R * O · B ₂ O ₃ ■ QO ₂ ,

where R, O is an alkali, alkaline earth and / or heavy metal oxide, χ the number 1 or 2 and QO _{2 is} silicon or germanium oxide which has a miscibility gap in the molten state, whereupon the preform is at a temperature of 500 to 600 ° C is tempered until two phases with microstructure have formed, whereupon this preform is _{treated with an acidic, aqueous solution to selectively dissolve the SiO 2-} poorer phase, then washed, dried, heated to close the pores and finally drawn to the fiber, which characterized in that the _{preform, which is porous due to the leaching out of the SiO 2-} poorer phase, is subjected to a treatment and, in order to change the oxidation state of at least one of the transition metal impurities contained therein, whereupon filling compounds are introduced into the pores before the porous preform is dried is heated to temperatures of 700 to 950 ⁰ C until the pores have closed.

Preferred embodiments of this method are given in claims 2-11.

A process for phase separation and solution is described in detail in US Pat. No. 2,221,709. This Process has been used for many years to produce a glass that is suitable for chemical purposes is. This process can be used to make a core that is suitable for many uses. The core must be coated with a coating material that has a lower refractive index. Because the refractive index of the core is quite low, the coating material remains on plastics and inorganic glasses with it limited refractive index. This process results in a glass with a significant water content. The end product is therefore partially separated, which leads to scattering losses and extremely high absorption (due to the OH vibrations) at 0.95 μΐη (of the order of 2500 dB / km). Additionally be not all transition elements are removed or oxidized after the process; this results in Absorp- I

tion values over 400 dB / km for 0.59 μm and 2000 dB / km for 1.05 μm. |

By using raw materials of higher purity than those used in the usual process and by separating the water these losses can be greatly reduced. By certain Modifications to the process can be used to produce glasses that reduce absorption and scattering losses are reduced to such an extent that the glasses can be compared to pure silica. They are therefore for all purposes suitable In addition, the refractive index of the glass can be changed by changing the composition of the starting materials, such as an exchange of germanium dioxide for silicon dioxide, set over wide ranges will.

This possibility of adjusting the refractive index results in a great adaptability to optical

Requirements. For example, the glass produced by the method of the invention can be used for the vein

or the cover of the fiberglass, or both. This results in angles of incidence that are significantly larger than known optical fibers made by chemical separation processes getting produced.

An important aspect of the present invention is the uncompacted porous process step Glass. The porous state of the glass is advantageous in several ways:

1. Because of the large surface area in relation to the volume, the oxidation-reduction of the remaining Transition elements are carried out with good efficiency;

2. For the same reason, the remaining water chemically bound to the glass can be removed.

3. Upper drawing compounds can be used to adjust the refractive index and other physical properties in the pores are entered.

In the case of a conductor provided with a coating, the mass can be the coating and / or the core can be added to obtain a composite fiber in which the refractive index of the vein is that of the Coating exceeds

In the manufacture of self-focusing fibers in which a radial change in the refractive index is to be achieved, the mass can be applied non-uniformly in order to achieve this radial change. When applied more or less uniformly, some of the composition can optionally be removed to obtain the desired index change. The amount that can be achieved by which the refraction changes is greater than was previously possible with the use of ion exchange technology. The ion exchange technique can only be used with a limited number of elements whose lov.sr. are interchangeable (e.g. Tl, Li, Na, K, Ru, Cs, Ag). In the present invention, there is no limitation on the type of atom that can be used as the filler material as long as the filling method is used (e.g., Ge and Pb can cause the refractive index to change twice as large as that possible by ion exchange). GeO2 or other network formers can be added to the original melt or as a filler in the pores. When added to the original melt, they are purified by the Phasil process, resulting in a smooth change in the refractive index. If they are introduced into the pores as a filler material, it must be of higher purity, but there is the advantage that a radial change in the refractive index can be achieved. Optionally, sodium or potassium ions can also be exchanged for a part of certain filling compounds in order to radially change the refractive index.

A generally applicable method for producing a porous glass with subsequent filling and forming an optical fiber includes the following measures:

(1) forming a rod or tube of desired dimensions from a borosilicate glass;
(2) heating the rod or tube for a period of time to convert the glass into high-silica and low-silica phases with defined and interconnected microstructures;

(3) dissolving or leaching out the low-silica phase using a mineral acid;

(4) Cleaning, if necessary, of the residues remaining in the pores formed during the dissolution by means of NaOH or dilute HF;

(5) treating the pores with aqua regia, if necessary, to remove circuit board inclusions;

(6) filling the pores, if desired, with iron-free filler;

(7) drying;

(8) Thermal sealing of the porous body (for example a rod, as above, inside a treated tube or the rods or tubes alone);

(9) heating and drawing the preformed structure into a fiber of a desired diameter; and
(10) Passing the fiber through a molten salt bath where the ion exchange with the filler mass takes place.

Steps (1) to (4) are used to produce a silica structure with a desired refractive index. This structure is sufficiently iron-free for use as an optical fiber. Stage (5) solves the main problem the light scattering to the outside due to circuit board inclusions.

The next four stages allow filling compounds free of transition elements to be introduced into the glass at low cost, by

(a) (step 6) introducing the filling compound into the pores in contrast to introducing it into the silica structure;
(b) (stage 8) heat treatment in a set atmosphere at temperatures below the closing temperature with effective control of the oxidation-reduction state of the remaining transferring rivet impurities, and

(c) (Step 9) thermal fusing of the filling compound with the silica structure. ί ·

Stages (6) to (9) are referred to as molecular filling in order to distinguish them from ion exchange ii,

the. In the filling process, the pores are not necessarily completely filled. Level (7) redeems. ":

Another important production problem: If the drying process takes place in a particularly reactive atmosphere 5! · ■

sphere is carried out, the separation results of protons, not only from the pores, but _^also:

(because of the favorable surface-to-volume ratio) from the glass structure itself.; ■

By adjusting the original composition of the melt and / or by using the replenishment process %

rods and tubes can be produced with a uniform but fixed refractive index so that they '},',

can then be used as a preform for the manufacture of a coated fiber, wherein the core has an io: i |

has a higher index of refraction than the coating. Additionally, controlled diffusion or other means allow one uneven filling of the pores in the silica structure, so that, for example, the filler concentration (e.g. B2O3 or AI2O3) changed from the center of the fiber radially outwards to the surface of the fiber. These Change in filler concentration is after fusing by heat treatment, whereby the pores are closed, permanent and leads to the radial change in the refractive index. This radial change the refractive index comes about by a completely different mechanism than in the ion exchange process, in which the ions are exchanged in the glass structure, e.g. B. according to US-PS 36 50 598. While a very limited number of types of ions can be used with the usual ion exchange processes and the extent of the ion exchange is limited by the number of ions already present in the structure, the filling method according to the present invention is only limited by the pore volume that makes up approximately 50% of the total volume.

The present invention makes use of the fact that the phased regions are in contact with one another Connect, whereby diffusion into any part of the porous glass structure is possible. The heat treatment, which causes the phase separation, can be used to adjust the pore size and thus the amount of diffusion can be used (see US-PS 35 49 524).

For the practical implementation of the method of the present invention, a porous medium is produced from a suitable starting glass which can be separated into phases and whose composition _{lies in the known range of the pseudo-ternary system R 1} O · B2O3 · QO2. This range includes those compositions which separate into at least 2 phases on heat treatment, one of which is easily decomposable and the other essentially irreplaceable. The component QO2 means silicon dioxide or germanium dioxide or any combination thereof. The component R _r O means an alkaline earth, alkali or heavy metal oxide, e.g. B. Li ₂ O, Na ₂ O, K ₂ O ₁ Tl ₂ O, CaO, BaO, MgO, BeO, SrO, PbO or ZnO or any combination thereof, where χ is the number 1 or 2, depending on the valence of the Metals R. The starting mixture can preferably be of the type described in US Pat. No. 2,10,6,744 and 2,215,039, for example. It is important that the mixture of the selected oxides has a miscibility gap and that the melt of the oxides is essentially a homogeneous liquid above a certain temperature and separates into at least two immiscible phases below this temperature has such a miscibility gap, a volume ratio of the phases between 1: 2 and 2: 1 is also important, as well as the fact that the chemical resistance of the phases deviates from one another, so that selective dissolution is possible.Typically suitable oxide mixtures are starting glass compositions that contain silica in quantities contain from 40 to 83 wt .-%, R ₁ O is z. B. as soda, potash, lithium oxide, etc. in amounts of about 2 to 10% and boron oxide in amounts of about 8 to 48 wt .-%. The iron content of the raw material should be kept below 10 ppm.

In addition to the borosilicate glass mentioned above, many other glasses, e.g. B. 5-20% Li ₂ O and 80-95% SiO ₂ . or 5-15% Na ₂ O and 85-95% SiO ₂ , a miscibility gap and are usable.

It has also been found that 0-20% by weight of germanium oxide GeO ₂ , or other network-forming oxides, can replace some of the silica in the starting glass.

The method of making the glass structure with separate phases connected to each other and the compression of this structure can be divided into the following stages:

a) molten glass,

b) phase separation,

c) detachment and

d) compression.

55 a) Glass melt:

An Na _{2 O-B2O3-SiO2} composition is chosen so that a homogeneous glass can be easily produced at 1400 ⁰ C that the mixture has a viscosity of around 10 to 10 ² Pa s · at 1400 ° C it has be used conventional glass melting process A modification of the invention is the addition of an oxidizing agent, such as a nitrate, to the glass melt. As a result, all transition metal impurities are oxidized to the highest level, which facilitates their separation. Some of the SiO _{2 can also be} replaced by another network former, such as GeO ₂ , in order to adjust the refractive index if necessary. For example, adding 10% GeO _{2 changes} the index by 1%.

A preferred embodiment of the starting glass is:

Mol%

more generally more preferred

Area area

SiO ₂ + GeO ₂ 40-80 45-70 B ₂ O ₃ 15-50 20-40 Alkali (Na ₂ O) 4-11 4-9 AI ₂ O ₃ 0-5 0-3

The preferred range contains 0-20 mole percent GeO ₂ .

Depending on the composition of the starting mixture, the glass is ^{heat-treated at a temperature of about 500 to 650 0} C for a few seconds to several weeks, so that it separates into two phases that are completely connected, and a microstructure with an average size of 100 · 10 ^{| ü} to 2000 · 10 ^-10 m, preferably between 100 m · 10- '° to 500 x 10 ~ ¹⁰ is present.

These dimensions are much smaller than the radius of the preform. Therefore, if the preform of the thermal Is subjected to compression stage, the diffusion quantities are so large that the filling compound, which is described below is embedded homogeneously in the silica structure in the microstructure. Changes can also be made in the filling compound concentration over distances in the order of magnitude of the preform radius.

Extensive studies on the kinetics of phase separation in the Na ₂ OB ₂ O ₃ -SiO _{2 system} have made it possible to achieve a maximum of connection between the phases. One of these phases consists mainly of covalently bound SiO ₂ and is referred to as the "hard" phase. The other phase includes the

Main amount of sodium and boron oxides in the original glass fiber with significantly less silica than in the hard phase. It is predominantly ionogenic in nature and is referred to as the "soft" phase. It has been found advantageous to carry out the heat treatment at the lowest temperature possible. This reduces the possibility of the rod or tube deforming from viscous flow. This also increases the difference in the composition of the two phases. When GeO ₂ or other network formers are added, they usually go into the hard phase.

The ionic impurities in the glass are mainly deposited in the soft, ionic phase. After this soft phase has been dissolved out, there is a reduction in the absorption loss the preferred distribution of the transition elements during the phase separation. This preferred distribution of ionic impurities increases when they have been oxidized to the highest valence level,

Because the ionic strength of the impurities increases, it facilitates the oxidation of the iron in the

Glass melt its separation. It also reduces the amount of ferrous ions, which are mainly

for the absorption losses in the frequency range of 1 μπι are responsible. It was found that the Absorption losses at 1 μπι can be reduced from 5000 dB / km to less than 100 dB / km.

The borosilicate glass in the form of tubes or rods is first subjected to an acid treatment.

Dilute solutions, preferably 1 η to 2 η solutions, of mineral acids such as HCl, H ₂ SO ₄ , HNO3 are used. However, hydrofluoric acid should not be used as it dissolves the high silica hard phase. The temperature of the solution bath is generally about 90-100 ° C, with about 95 ° C being preferred. If the temperature of the bath falls below 90 ° C, this deteriorates dissolution and the solution time is substantially long. Less than 85 ⁰ C, the dissolving too slowly. the solution time is dependent on the acid concentration and the bath temperature up to a certain degree. a characteristic release pattern comprises a two-day treatment of the glass with a 1.5 η solution of nitric acid at about 95 ° C, then cleaning in a fresh solution of the same acid concentration and a subsequent one-day final cleaning in a dilute, 0.2 η nitric acid solution.
Sometimes it may be desirable to etch the glass before loosening it to remove the surface skin and thereby achieve more even penetration, which is recommended for thick-walled tubes and if the glass has become contaminated in storage The characteristic preheating can be carried out by immersion in a 15% strength by weight NH ₄ F · HF solution for a period of 10 minutes. Usually the silica-rich phase remains while the silica-poor or boron-rich phase is removed upon dissolution with an acid

It was found that the pores of the resulting silica-rich hard phase skeleton approximately to Half are filled with colloidal silica, which is a decomposition product of the separated microphase It is usually advantageous to separate this colloidal silica in order to render the transition elements eliminate that may have been reflected here. After washing the hard, porous skeleton in an aqueous solution is the skeleton with a solvent for colloidal silica, preferably one dilute solution of HF / HCl acids or sodium hydroxide, treated for a period of time is sufficient to remove the colloidal silica itself without significantly attacking the skeleton. Usually the treatment with the solvent for colloidal silica takes about 1 to 4 hours. After this Has been done, the pores can be treated with hot aqua regia to all possible Remove circuit board connections that may be present. Eliminate the acid treatments described above Traces of transition elements from the silica gel as well as from the microstructure surface. Then it can Skeleton to be dried. The dried skeleton consists of a solid structure that is connected with a System of interconnected pores is provided which is essentially free of contaminants are.

It was found that if GeO _{2 is added to} the melt instead of some S1O2, enough GeO2 remains in the hard phase (unassailable by the HCl solution) to cause a noticeable increase in the refractive index. This can be used to adjust the refractive index of the product so that it is higher and lower than that of the commercially available products. Other network-forming oxides can also be used for this purpose.

The process stage of the compression consists in heating of the skeleton to 700 to 950 ⁰ C, depending on the glass composition, so that the pores of the skeleton to be closed by viscous flow, whereby a homogeneous glass of the hard phase remains. It has been found that if the densification is carried out as described in US Pat. No. 2,221,709, a glass with unacceptable optical losses results. It has also been found that the cause of these losses is the incomplete removal of acid and water from the pores before they collapse. It has been found that most of the inhomogeneities in the glass can be caused by the presence of water, removed when the glass is held at 500-700 ⁰ C 15 to 50 hours before it reaches 700-950 ⁰ C. is heated. This drying process is preferably carried out in a reactive atmosphere (such as CCI4, CI2 or SiCU).

In addition, we found that it did not compact during the heat treatment at 500 to 700 ° C Glass can be influenced very strongly. This is possible due to the large surface area that is available at this stage is present. This is to be understood as follows: Although the oxidation of the ionic impurities is theirs Separation in stage b) facilitated and the absorption at 1 μπι reduced, for example from the residual iron is caused, can be a lower attenuation in the range of 6 μπι by reducing the reach ionic impurities. For example, by reduction shortly before compaction by heating the porous glass for 14 hours in a vacuum, the attenuation of 250 dB / km 18 dB / km reduced. The exact effect of the oxidation-reduction treatment depends on which one ionic impurities are present in the porous glass.

According to another preferred embodiment of the invention, the field of use of in Phase separated porous glasses for the production of optical fibers by incorporating a filler into the Enlarged pores. When using a filling process, the refractive index of the glass core can be reduced to one usable value can be reduced. In practice this can be done in a number of ways. After a suitable method is the rod or tube of the desired size by whole or in part Immersion impregnated in a solution containing a salt or a compound of an element, its oxide should be stored. The percentage of oxide that is to be absorbed can be changed by changing the treatment solution. Considering the composition, density and porosity of the porous glass knows, the concentration of a solution that is required for a desired final glass can be calculated. the The porosity of the porous glass can be determined by the usual methods; it is usually around 50%. Easily soluble compounds are preferred, and the solution is, if necessary, heated to improve solubility. Some compounds tend to volatilize when theirs Solutions are heated; to avoid this and to maintain the desired high concentration, these solutions can be housed in a closed container during the impregnation stage.

The filling compound is deposited in the form of, for example, carbonates, nitrates or hydroxides, which give the corresponding oxides when heated. Preferred filling compounds are those compounds of the alkali metals, alkaline earth metals, boron, germanium, aluminum, titanium, lead, bismuth and Cers + ³ or Cers ⁺⁴ , which convert into the corresponding oxides during the thermal compression stage. With the exception of boron oxide, which lowers the index of refraction, all other oxides increase the index of refraction of the preform glass. The filling compound is preferably added in an amount of about 5-30% by weight, based on the weight of the unfilled preform.

In the case of making an overlay for use with a fused silica core, The index of refraction can be increased by increasing the B ^ content of the phased tubular cover to be humiliated. For example, the porous tube for making the coating is turned into a saturated one Solution of ammonium borate immersed in a molten silica rod is then inserted into the tube, and the combination of dust and pipe is then thermally compacted

Another example of the use of padding is the manufacture of a preformed rod with a corresponding uniform concentration of filler material, which after drawing to the fiber means Ion exchange is treated.

In this case, the starting glass and the process steps are the same as in the previous ones Examples, however, level (6), padding, is different. Here you impregnate the porous rod with a colloidal solution of aluminum particles in LiOH. This results in a lithium-alumina-silicate glass that is after The fiber formation can easily be treated by ion exchange to make a self-focusing fiber result because the ion exchange process has a refractive index that is radially from the center to the Outside surface changes

Another application of the padding process is the manufacture of a self-focusing fiber by Direct production of a preform whose refractive index varies radially from the center to the outer surface changes and which, when drawn to the fiber, maintains this radial change in refractive index

This can be done in a number of ways. For example, a colloidal suspension of an oxidic Filling compound (e.g. AI2O3 or GeÜ3) diffuse into irregularly shaped pores, if the pores of such are small in size that there is a steric hindrance to the flow of the suspended particles Diffusion time can be regulated in order to achieve the desired radial concentration profile of the filling compound in the To reach pores.

Another method relates to the use of two reaction components that a filler on the Precipitate the walls of the pores. It begins with the one reaction partner in a porous tube

inside the tube and the other outside the tube. When creating the hydrostatic Pressures and concentrations as functions of time, the amount of precipitation varies with radial Distance from the inner wall.

After the filling compound has been introduced into the pores, it is dried and compacted as above 5 described.

example 1

To produce the vein of a coated preform, a melt of high-purity chemicals ίο (ie less than 10 ppm total transition metal ions) is prepared. 70 mol% SiO ₂ , 7 mol% Na ₂ CO ₃ and 23

1 · mol% B ₂ O ₃ are melted in a platinum crucible at 1400 ° C. For this purpose, 0.1%

ij NaNO ₃ given. The melt is stirred until it is homogeneous. After the refinement, a rod of 5 mm

? ^f diameter drawn. The rod is subjected to a heat treatment at 55 ° C for 4 hours. the

The microstructure has a size of about 500 x 10- '° m. The rod is in a solution for 72 hours at 95 ° C

i. \ 15 treated by 3 η HCl and then washed in ion-free water. Water and acid must not contain any

Put% in the glass. The glass is then immersed in a 2% HF solution for two hours at 22 ° C,

I treated with 3 η HCl and then washed with water. The porous rod is only dried at 100 ° C in order to achieve the

% to remove large amounts of water, and then at 550 ° C to separate the remaining water. The stick will

S then slowly heated to 850 ° C; the temperature is enough to close the pores and the impregnated

I 20 to convert glass into an essentially homogeneous, glass body. This rod is attached to a usual

'if attached fiber drawing device, drawn into a fiber with a refractive index of 1.46 and in per se

| j coated in a known manner with a plastic with a low refractive index.

j | Example 2

'% This example describes the manufacture of the core of a coated preform with a larger one

K * refractive index than in Example 1, so that there is more freedom in choosing a coating which is a lower one

ί Must have refractive index than the wire. The melt is made up of high purity chemicals (i.e. less

% than 10 ppm of total transition metal _{ions) and contains 58.2 mol% SiO 2} , 10 mol% GeO ₂ , 25.4 mol% B ₂ O ₃ fi 30 and 6.4 mol% Na ₂ O. It is melted in a platinum crucible at 1400 ° C. These are used as an oxidizing agent

5 0.1% NaNO ₃ given. The melt is stirred until it is homogeneous. After refining, a stick of

■ {■; 3 mm diameter drawn. The rod is treated at 550 ° C for 4 hours. It will then last 48 hours

/ - Dissolved in 3 η HCl at 95 ° C. and then washed with ion-free water.

';' 35 B e i s ρ i e 1 3

· A melt of high-purity chemicals is prepared (ie less than 1 ppm total transition metal ions). 70 mol% SiO ₂ , 7 mol% Na ₂ CO ₃ and 23 mol% B ₂ O ₃ are melted in a platinum crucible at 1400 "C and stirred until homogeneous. After the refining, a tube with an internal diameter is

40 water of 2 mm and an outer diameter of 6 mm. The tube is at 580 "C for 100 hours

j The heat treated microstructure has m size of about 800 · L0 ^10th A short course

Hydrofluoric acid is turned on around a thin layer of highly siliceous glass on the

Remove surface of the tube. The tube is then dissolved in 2η HCl at 95 ° C. for 48 hours. That The water used and the acids must not bring any impurities into the glass. The glass will continue

45 immersed in a 0.5 η NaOH solution at 22 ° C for 6 hours, with water that passed through a fine-pored filter ■ has been sent, washed to neutrality and then treated with cold 3 η HCl This porous tube

is then immersed in a solution containing 1500 g of boric acid, 700 ecm of 28% ammonium hydroxide and 1000 ecm Water contains the porous tube is dried and while drying with carbon tetrachloride vapors treated to remove all chlorine residues. A molten silica rod is pushed into the tube

50 and the combination rod-tube-preform slowly heated to a temperature of about 850 ° C, the sufficient to close the pores and the impregnated glass in a substantially homogeneous vitreous Convert body. As the temperature at which this takes place affects the introduced oxide or the Oxides changes, no universal temperature for heating can be specified, but the appropriate temperatures can easily be determined by experiments for other combinations; there are temperatures of

55 800-900 ° C applicable. In any case, you will find that they are much lower than the temperatures which are required to make a glass of equivalent composition directly from the starting materials to melt. This preform is then drawn into coated fibers.

B e i s ρ i e 1 4

Ί ' _: This example shows the deposition of filling compounds by vapor deposition.

, Ϊ The germanium tetrakis isopropoxide was first produced using the method of Bradley and co-workers (J. Chem. Soc 1951, p. 280).

; ⁶⁵ C ₆ H ₆

«Ι GeCl ₄ + 4 C ₃ H ₇ OH + 4 NH ₃ ► Ge (OC ₃ HT) ₄ + 4 NH ₄ Cl

Highly pure GeCl ₄ of 99.999% should be used. The Ge (OC ₃ H ₇ ^ is further purified by means of a gas chromatography column according to the technique described in Analyt Chenu Volume 41 (1969), page 1243. The Ge (OH ₃ H ₇ ) 4 vapor emerging from the gas chromatography column then diffuses into it porous Silicatrohr by ^J about the inner surface and at the same time, water vapor diffuses into the tube through the outer surface, the thermal decomposition in accordance with:. 5

2 H ₂ O + Ge (OC ₃ H ₇ ), > GeO ₂ + 4 C ₃ H ₇ OH

ei gives a precipitate of GeO?, the concentration of which in the pores drops radially towards the outer surface. This tube is then ^{heated very slowly to 950 °} C. It is kept at this temperature until it becomes transparent, which indicates the compression, and drawn out to the fiber.

Example 5

This example relates to the deposition of a filling compound through the formation of precipitates through reaction between two solutions within the pores of a preform. Highly pure Al ₂ O ₃ , which can be purified by gas chromatography as in Example 2, is dissolved in NaOH. The solution is placed in a porous tube. A dilute HCl is brought around the outside of the tube. When the two solutions come into contact within the pores, Al (OH) _{3 is} precipitated.By adjusting the difference in hydrostatic pressures and the concentration as a function of time, the radial change in the filling mass can be adjusted . As soon as the desired filling compound concentration - 10 mol% Al (OH) ₃ - has been reached, the preform is washed, first with dilute HCl to remove all remaining sodium ions, then with distilled water, which is removed from all scattering by means of a fine-pored filter Particle has been cleaned. The preform is then ready to dry, close pores, compress and draw out the fiber. 25th

Claims (11)

Patent claims: 1. Process for the production of conductors for optical signals, consisting of a core with a Cover layer, the refractive index of which is lower than that of the core, by drawing a preform the melt of a glass of the pseudo-ternary system Ä, O · B ₂ O ₃ · QO ₂ , where R, O is an alkali, alkaline earth and / or heavy metal oxide, χ the number 1 or 2 and QO _{2 is} silicon or germanium oxide, which has a miscibility gap in the molten state, whereupon the preform is at a temperature of 500 to 600 ⁰ C is tempered until two phases with microstructure have formed, whereupon this preform is treated with an acidic, aqueous solution to selectively dissolve the SiO2-poorer phase, then washed, dried, heated to close the pores and finally drawn into fibers, thereby characterized in that the preform, which is porous due to the leaching out of the SiOi-poorer phase, is subjected to a treatment in order to change the oxidation state of at least one of the transition metal impurities contained therein, whereupon into the pores before the porous preform is dried to temperatures of 700 to 950 ⁰ C is heated until the pores have closed, filling compounds are introduced. 2. The method according to claim 1, characterized in that the glass melt has an oxidizing agent is added. 3. The method according to claim 1 or 2, characterized in that the preform is _{immersed in a 15 wt .-% aqueous NH 4} F - HF solution for 10 minutes before being placed in the mineral acid bath. 4. The method according to claim 1 to 3, characterized in that the porous preform according to the Subsequent washing with a solvent for colloidal silica for the acid treatment Duration of 1 to 4 hours is treated. 5. The method according to claim 1 to 4, characterized in that the porous preform on a Temperature that is 100 to 300 ° C below the temperature of thermal compression is heated. 6. The method according to claim 5, characterized in that the porous preform is first ^{heated to a temperature of 500 to 700 0} C and then to a temperature of 700 to 950 ° C for a period of 15 to 50 h. 7. The method according to claim 1 to 6, characterized in that the porous preform before the last Heating in an aqueous solution of filler compounds, which in the subsequent heating in the Refractive index of the porous preform influencing oxides pass over, is immersed. 8. The method according to claim 7, characterized in that the aqueous solution, the filler compounds in amounts of 5 to 30% by weight, based on the weight of the porous preform will. 9. The method according to claim 7 and 8, characterized in that the in the pores of the porous preform diffused filler compounds are precipitated in the pores. 10. The method according to claim 9, characterized in that the filling compound directly on the surface of the porous preform deposited and the preform then deposited up to a portion of the Filling compound has penetrated deeper into the porous preform, is heated. 11. The method according to claim 7 to 9, characterized in that the part of the in the porous preform evenly distributed filling compound, which is located near the outer surface of the porous preform has deposited, is partially dissolved out again.